Process for tanning skins



Oct. 16, 1956 A. E. USHAKOFF 2,767,043

PROCESS FOR TANNING SKINS Filed Jan. 12, 1953 V INVENTOR. ALEXIS E.USHAKOFF gzmgw, 3 4m 11412:

ATTORNEYS United States Patent PROCESS FOR TANNING SKINS Alexis E.Ushakolf, Beverly, Mass, assignor to Secotan, Inc., Somerville, Mass., acorporation of Massachusetts Application January 12, 1953, Serial No.330,632

14' Claims. (Cl. 8-15059' The present invention relates to the tanningof animal skins and the like and provides improvements to tanningprocesses during which a water-miscible organic solvent is forcedthrough the skin to extract and replace the water. Such processesapplied to the formafion of molded hollow leather articles are disclosedin my U. S. Patent No. 2,582,298 and my copending application Ser. No.233,923 filed June 27, 1951, now Pat. No. 2,704,238; and applied to theproduction of flat leather in my copending application Ser. No. 233,924filed June 27, 1951, now Pat. No. 2,702,229.

In these tanning processes a water-wet skin is supported on a poroussurface of a filter material such as wool felt, plaster of Paris orother material of equivalent fine porosity. The surface may be flat toform flat leather, or concave to form hollow leather articles. Awatermiscible organic solvent is then forced through the skin and thesupporting surface until substantially all the Water in the skin hasbeen extracted. Thereafter the skin is treated under substantiallynon-aqueous conditions until it is finally tanned, as by forcing tanningagents, and neutralizing agents through the skin and the supportingmember. In this manner, the time required for complete tannage isreduced to a few minutes, and in addition, the skin may be dried rapidlywithout the precautions necessary to produce soft pliable leather fromskins treated in aqueous tanning solutions, and without being fatliquored.

A difficulty sometimes encountered in such processes arises from thefact that the water-wet skin is not uniformly permeable. When thesolvent is applied, it first permeates the more permeable regions,extracting the water from them and rendering them even more permeable.Thereafter, the solvent applied to the skin tends to channel throughthese regions leaving other regions substantially untreated. A furtherdifliculty which results from the forcing of the tanning agents throughthe skin while it is supported on a porous surface of a filter material,such as wool felt, plaster of Paris or material of equivalent fineporosity, is the precipitation of tanning agent in the pores of thesupporting surface which clogs them. Such finely porous materials aredesirably used to support the skin during the solvent treatment sincethey may be formed with a smooth appearing surface. As pointed out inPatent No. 2,582,298 the configuration of the surface is imparted to theskin during the solvent extraction operation and this fact rules out theuse of more coarsely porous materials. The present invention overcomesthese difficulties and in addition reduces the number of steps performedin the apparatus in which the skin is supported, thus enhancing theproductivity of the apparatus.

According to this invention the skin, prior to treatment with theorganic solvent, is treated with an aqueous solution of an inorganic ormineral tanning agent, and if desired the tanning agent is neutralizedin the skin. Alternatively, the tanning agent is left unneutralized inthe skin to be subsequently neutralized after the water has beenextracted. V

The effect of such a treatment is to improve the permeability of theskin and render is substantially uniform.- Thus, not only is selectiveextraction of the water in the more permeable regions avoided, but lesssolvent is required for the extraction. In addition, the Water Wet skin,although containing tanning agents, is still semiplastic like anuntanned skin, and it may be molded to form hollow articles, such asshoe uppers, in the manner disclosed in my U. S. Patent No. 2,582,298.Apparently the skin does not become finally tanned until it has beendried.

It will further be seen, that, because the tanning agents areincorporated in the skin before it is further treated on the supportingporous surface, the tanning agents are not forced through the poroussupport and the danger of their precipitating in the pores is avoided.

An additional feature which may be used with the process of thisinvention is the incorporation of a fatty acid in the skin after thewater has been extracted and before the skin has been dried. This isaccomplished by dissolving a fatty acid in a suitable solvent andforcing the solution through the skin while it is supported on theporous surface, and results in a marked increase in the tensile strengthof the skin without rendering it greasy. If on the other hand, the skinis dried without the addition of a fatty acid, the subsequent additionof fatty acid does not substantially enhance the tensile strength butrenders the skin greasy in feel and appearance. Ordinary fat liquoringcompounds, such as neetsfoot oil, may also be added to the skin, butWithout imparting the beneficial effects of the fatty acid. The efiectsof fat liquoring are thus realized in the process of this invention,While the critical control over pH necessary for fat liquoring by theconventional aqueous tanning operations, is avoided.

In general, this invention consists first in treating a skin, which maybe pickled, bated, or fresh, with an aqueous tanning bath of aninorganic or mineral tanning agent such as chrome, iron, titanium,zirconium, or the like compounds, to introduce the tanning agent intothe skin. Preferably, to accelerate the treatment, the temperature ofthe bath is increased and maintained at a point about 20 F. below theshrinkage temperature of the skin. The aqueous treatment may terminatewith the neutralization of the tanning agent in the skin, as by theaddition of a base to the tanning bath, or if desired neutralization maybe delayed until after the skin has been dehydrated with the organicsolvent.

After the tanning agent has been incorporated in the skin and While theskin is still wet, it is placed on and in contact with a supportingporous surface and the organic solvent is forced through it to extractthe water.

The skin is then treated with an organic solvent solution of a fattyacid, and dried. If the tanning agent has not been neutralized prior todehydration, a base may be added to the organic solvent used fordehydration, or if desired, dehydration may be followed by a separatetreatment of the skin with an organic solvent solution of a base, or thebase may be included in the fatty acid solution.

It will be apparent from the foregoing general description that thisinvention lends itself to a multitude of variations. In the followingexamples, representative and preferred embodiments of this invention asapplied to the production of molded shoe uppers are described in detail.

In the drawings:

Fig. 1 shows in cross-sectional elevation a suitable mold for formingshoe uppers, and

Fig. 2 is a perspective view of a typical shoe upper produced by theprocess of this invention.

7 Example 1 A wet bated skin was pickled, then treated in an aqueoustanning bath and neutralized to insolubilize the tanning agents andwashed in Water. While still freshly wet,

a blank'of the skin was molded, dehydrated while in the V material, soldby Diamond Alkali Corp., Cleveland, Ohio,

and having the following analysis:

removed from the mold and dried in the air to render it completely andpermanently tanned.

' ExampIe'Z A wet bated skin was pickled, treated in an aqueous tanningbath, then molded and dehydrated in the mold.

The tanning agent in the molded blank was then'neutralized in the mold,and the skin was finally fat liquored and dried. a e

The skin was treated as described in: Example 1, supra, to the pointjust after; the tanning agent was added to the drum and allowed topenetrate through the skin. Without neutralizing the tanning agents, theskin was re- V moved from the drum and cut intov appropriate blanksPercent CI'zOs i 23.5 Hydrolyzable SOs 20.8 A1203 1.6 NazSOa 51.8Basicity 42-44 was dissolved in hot water to a concentration of about20% by weight and added to the drum, and the skin was tumbled untilthetanning solution had fully penetratedthe skin during which time thetannning bath was heated to about 140 F. as the shrinkage temperature ofthe skin rose to about 160 F. Sodium bicarbonate was thenadded slowly tothe drum until the pH of the solution reached 3.8-4.0 during which timethe tanning bath was heated to about 160 F. The skin was then removedfrom the drum, washed infresh water to remove excess dissolved salts,and cut into blanks of appropriate shape and size to fit the mold.

A blank of the skin was then placed in the apparatus shown in Fig. 1 tobe molded. The apparatus consisted of a box-shaped casing 10 containingthe mold 12 and provided with a cooperating cover 14 having a fluidinlet tap 15. The casing 10 engaged the cover 14 along 'a peripheralflange 16, and supported the mold at its marginal edge on a recessedperipheral shoulder 17. The

' mold was constructed of a. porous material, such. as

plaster of Paris or other suitable ceramicmaterial, and was providedwith a concave molding surface accurately conforming to the shape of ashoe last. Inthe construction shown the mold was supported on theshoulder 17 of the casing10 on a soft gasket '18, while the body of themold rested on sand 19 with which the casing 10 was filled. A dischargeconnection 20 covered witha screen 22 connected into the bottom of thecasing '10-atany convenient location. I 7 r The cover 14 engaged thecasing along its marginal surface 21 which cooperates with the flange 16of .the

casing.

The wet skin 23 was placed over the mold with its marginal edgesoverlying the peripheral flange 16,- and the cover was clamped inposition by conventional means V slowly, but as the water was extractedby the acetone the flow increased considerably. The. flow of acetone wascontinued until the skin was substantially dehydrated as was indicatedby a specific gravity no more than 0.792 at 70 F. for the acetone. wasnext fat liquore'dby forcing an acetone solution containing 7% by weightof oleic acid through the skin while itwas; supported in the. mold. Theblank then in the molded form of;a.1shoe upper, as shown in Fig. 2, was;

The dehydrated molded blank' which were molded and dehydrated in themanner described in Example 1. The molded and dehydrated skin was thensimultaneously neutralized and fat liquored by forcing through it 500cc. of an acetonesolution containing 7% by weight. of oleic acid. and 10cc. of triethanolamine. The skin was then removed from "theimold anddried to render. itcompletely and permanently tanned. i

Example 3 A pickled calfskin was treated in an acidic aqueous tanningbath then, before'the tanning agent was neutralized, removed from thebath, and cut into shoe upper blanks. A blank, while Wet with water, wasthen molded to shoe upper form, dehydrated, neutralized, fat liquoredfand dried.

A pickled calfskin was drummed in twice its weight of 7 an aqueoussolutioncontaining 4 percent by Weight of salt and having a pH of-1.8'imparted; by adding sulfuric acid. When equilibrium was reached, 10percent, based A blank cut from the skinand wet with water was A Vmolded .under the pressure of acetone, and-dehydrated as described inExample 1. a Following the dehydration, the

tanning agent in the skin was. neutralized by forcing through theskin'whilestill in the mold, a solution consisting of: a

V 'Cc. Ammonia (concentrated commercial) 75 Acetone 500 The molded blankwas finally fatliquored with oleic'acid as described inExample2,"removed from the mold and dried. i

'The' foregoing examples describe 'indetail a representative few of themethods by which this invention may be practiced, and show the latitudein which the various stepsmay -be varied. For instance, neutralizationof the skin maybe .carried'out before, after or While 'the skin ismolded. It will also be. understood that inorganic or mineraltanningagents, other than chromium salts maybe used in invention, andthat water-miscible organic solvents other than acetone may be used forthe dehydration andv subsequent treatment, including lower aliphaticalcohols, and water-miscible polyalcohols, ethers,

andesters, examples of which are given in my-copending application:Ser.No. 233,923 filed June 27, 1951. Similarly, fatty acids other than oleicmay also be used for the; improved fat liquoringstep, including stearicacid, lauric acid; palmitic acid and the like.

It willalso be appreciated that for the purposes of this invention, theskin after dehydration need not beabsolutely anhydrous, nor must theorganic solvent solutions subsequently applied to the skin, so longassubstantially 7 all the. Water-is out of theskin. In this connection askin- 7 containing-less than about- 20%"by weightof water may beconsidered to'be dryfor purposes of this invention.

Although this invention has beendescribed in detail with reference tothe formation of shoe uppers, other leather articles, both molded andflat, may obviously be produced without departing from the scope of theinvention.

This application is a continuation in part of my copending applicationsSer. Nos. 233,923 and 233,924 both filed June 27, 1951.

Having thus disclosed my invention and described in detailrepresentative examples of the best manner known for practicing theinvention, I claim and desire to secure by Letters Patent:

1. In the method of tanning animal skins and the like wherein awater-wet skin is extracted of Water by forcing an inert water-miscibleorganic solvent through the skin in an amount sufiicient to extract andreplace substan tially all the water with the solvent, a mineral tanningagent is incorporated in the skin and the skin is finally dried ofsolvent with the mineral tanning agent neutralized therein: theimprovement comprising contacting the skin with an aqueous solution of amineral tanning agent to distribute the tanning agent throughout theskin before the water in the skin is extracted and replaced with theorganic solvent, thereafter supporting the skin upon and in conformitywith a porous surface of a filter material having a porosity at least asfine as wool felt, and then forcing the organic solvent under a fluidpressure differential through the skin in the direction such that thesolvent flows from the skin to the surface.

2. In the method of tanning animal skins and the like wherein aWater-wet skin is extracted of water by forcing an inert water-miscibleorganic solvent through the skin in an amount suflicient to extract andreplace substantially all the water with the solvent, a mineral tanningagent is incorporated in the skin and the skin is finally dried ofsolvent with the mineral tanning agent neutralized therein: theimprovement comprising contacting the skin with an aqueous solution of amineral tanning agent to distribute the tanning agent throughout theskin before the water in the skin is extracted and replaced with theorganic solvent and heating the solution to an elevated temperaturelower than the shrinkage temperature of the skin, and thereaftersupporting the skin upon and in conformity with a porous surface of afilter material having a porosity at least as fine as wool felt, andforcing the organic solvent under a fluid pressure differential throughthe skin in the direction such that the solvent flows from the skin tothe surface.

3. The method of tanning skins comprising contacting an untanned skinwith an aqueous solution of a mineral tanning agent until the tanningagent is distributed throughout the skin, thereafter supporting the skinupon and in conformity with a porous surface of a filter material havinga porosity at least as fine as wool felt, forcing an inertwater-miscible organic solvent under a fluid pressure diiferentialthrough the skin in the direction such that the solvent flows from theskin to the surface and in an amount to extract and replacesubstantially all the water in the skin with solvent, neutralizing thetanning agent by contacting the skin with a non-aqueous solution of abase, and finally drying the skin of solvent.

4. The method defined by claim 3 wherein the mineral tanning agent inthe skin is neutralized by forcing an organic solvent solution of a basethrough the skin while the skin is supported on the porous surface.

5. In the method of producing hollow leather articles wherein awater-wet skin is conformed by fluid pressure to the surfaces of asuitable concave mold having a depth substantially in excess of thethickness of the skin and the skin is then extracted of water by forcingan inert Water-miscible organic solvent through the skin in an amountsuflicient to extract and replace substantially all the water with thesolvent, a mineral tanning agent is incorporated in the skin and theskin is finally dried with the mineral tanning agent neutralizedtherein: the improvement comprising contacting the skin with an aque- 6ous solution of a mineral tanning agent to distribute tarining agentthroughout the skin before the skin is conformed to the mold surface,then forcing the skin by fluid pressure into conformity with the surfaceof a porous concave mold of a filter material having a porosity at leastas fine as wool felt, said mold having a depth substantially in excessof the thickness of the skin, and forcing an inert water-miscibleorganic solvent through the skin, while the skin is supported on theporous mold surface, under a fluid pressure diiferential in thedirection such that the solvent flows from the skin to the surface.

6. In the method of producing hollow leather articles wherein awater-wet skin is conformed by fluid pressure to the surfaces of asuitable concave mold having a depth substantially in excess of thethickness of the skin and the skin is then extracted of water by forcingan inert watermiscible organic solvent through the skin in an amountsufiicient to extract and replace substantially all the water with thesolvent, a mineral tanning agent is incorporated in the skin and theskin is finally dried with the mineral tanning agent neutralizedtherein: the improvement comprising contacting the skin with an aqueoussolution of a mineral tanning agent and heating the solution to anelevated temperature lower than the shrinkage temperature of the skin todistribute tanning agent throughout the skin before the skin isconformed to the mold surface, then forcing the skin by fluid pressureinto conformity with the surface of a porous concave mold of a filtermaterial having a porosity at least as fine as wool felt, said moldhaving a depth substantially in excess of the thickness of the skin, andforcing an inert water-miscible organic solvent through the skin, whilethe skin is supported on the porous mold surface, under a fluid pressuredilferential in the direction such that the solvent flows from the skinto the surface.

7. The method of forming hollow leather articles comprising contactingan untanned skin with an aqueous solution of a mineral tanning agentuntil the tanning agent is distributed throughout the skin andneutralizing the tanning agent to fix it in the skin, thereafter forcingthe skin by fluid pressure into conformity with the surface of a concaveporous mold of a filter material having a porosity at least as fine aswool felt, said mold having a depth substantially in excess of thethickness of the skin, and forcing an inert water-miscible organicsolvent through the skin, while the skin is supported on the porous moldsurface, under a fluid pressure differential in the direction such thatthe solvent flows from the skin to the surface and in an amount toextract and replace substantially all the Water in the skin withsolvent, and finally drying the skin of solvent.

8. The method defined by claim 7 wherein the mineral tanning agent isneutralized in an aqueous solution before the skin is extracted of waterwith the solvent.

9. The method of forming hollow leather articles comprising contactingan untanned skin with an aqueous solution of a mineral tanning agentuntil the tanning agent is distributed throughout the skin, thereafterforcing the skin by fluid pressure into conformity with the surface of aconcave porous mold of a filter material having a porosity at least asfine as wool felt, said mold having a depth substantially in excess ofthe thickness of the skin and forcing an inert water-miscible organicsolvent through the skin, while the skin is supported on the porous moldsurface, under a fluid pressure differential in the direction such thatthe solvent flows from the skin to the surface and in an amount toextract and replace substantially all the water in the skin withsolvent, neutralizing the tanning agent by contacting the skin with anon-aqueous solution of a base, and finally drying the skin of solvent.

10. The method defined by claim 9 wherein the mineral tanning agent inthe skin is neutralized by forcing an organic solvent solution of a basethrough the skin while the skin is supported on the porous mold surface.

are wherein a water-wet skin is extracted of water by forcing afi inertwater-miscible organic solvent through j the skin an amountsufiiciht toextract and replace substantially all the water with the solvent, a,chrome tanning'agent is incorporated in the skin and the skin isfinally dried, of solvent with the creme tanning agent neutralizedtherein: the improvement comprising 'contacting the skin with an aqueoussolution of a chrome 'tanning' agent to distribute the tanning agentthroughout the skin before the water in the skin is extracted and replaced with the organic solyent, thereafter supporting'the skin upon andin conformity with' a poroussurface of a filter material having" aporosity at least as fine'as wool felt, and then forcing the, organicsolvent under a fluid that the solvent flows from the skin to'thesurface."

7 12. In the method of tanning animal skins and the like wherein awater-wet skin is extracted of water by forcing acetone through the skinin an amount sufficient' to extract and replace substantially all thewater with the V acetone,; a' chrome tanning agent is incorporated 'inthe skin and the skin is finally dried of acetone with the chrometanning agent neutralizedtherein: the improvement comprising contactingthe skinrwith an aqueous solution of a chrome tanning agent todistribute the tanning throughout the skin before the water inithe skinis extracted and replaced with the acetone, thereafter supporting theskin upon and in conformity with a porous surface, of a filter materialhaving a porosity at'least as fine as wool felt, and then forcing theacetone under a fluid pressure differential through the skin in thedirection such that the acetone flows from the skin to the surface. p r

13. The method of tanning skins comprising contacting an untanned skinwith an aqueoussolution of a chrome tanning agent until the tanningagent is distributed throughout the skin, thereafter supporting the'skinupon and in conformity with a porous surface of a filter material havinga porosity at least as fine as wool felt, forc- 7 pressure differentialthrough the skin in the direction such ventthrough the skin, while theskin is supported on the an inert water-miscible organicfsolvent 'undera fluid pressure differentialthrough the skin in the direction such thatthe solvent flows from the skin to the surface and in an amount toextract and replace substantially all the water 'inttheiskin withsolvent, neutralizing-the tanning] agent by contacting the skin with anon-aqueous solution 7 of a base, and finally drying the skin ofsolvent.- 7

14. The method of forming hollow leather articles comprising contactingan untanned skin with an aqueous solution of chrome tanning agent untilthe tanning agent is distributed throughout the skin, thereafter forcingthe skin by fluid pressure intoconformitywith the surface of a concaveporous mold of a filtermaterial haw-1- ing a porosity at least asfineaswool felt, said Irnold having a depth substantially in excess ofthe thickness of the skin and forcing an inert'water-misc'ible organicsolporous mold surface, under a fluid pressure diiferential in thedirection such that the solvent flows from the skin to the surface andinan amount to extract and replace substantially all the water in theskin with solvent,rneutralizing the tanning agent by contacting the skinwith a non-aqueous solution of a'base, and finally drying the skin ofsolvent. 7

References Cited in the file of this patent UNITED STATES PATENTS GreatBritain of 1902'

1. IN THE METHOD OF TANNING ANIMAL SKINS AND THE LIKE WHEREIN AWATER-SKIN IS EXTRACTED OF WATER BY FORCING AN INERT WATER-MISCIBLEORGANIC SOLVENT THROUGH THE SKIN IN AN AMOUNT SUFFICIENT TO EXTRACT ANDREPLACE SUBSTANTIALLY ALL THE WATER WITH THE SOLVENT, A MINERAL TANNINGAGENT IS INCORPORATED INT HE SKIN AND THE SKIN IS FINALLY DRIED OFSOLVENT WITH THE MINERAL TANNING AGENT NEUTRALIZED THEREIN: THEIMPROVEMENT COMPRISING CONTACTING THE SKIN WITH AN AQUEOUS SOLUTION OF AMINERAL TANNING AGENT TO DISTRIBUTE THE TANNING AGENT THROUGHOUT THESKIN BEFORE THE WATER IN THE SKIN IS EXTRACTED AND REPLACED WITH THEORGANIC SOLVENT, THEREAFTER SUPPORTING THE SKIN UPON AND IN CONFORMITYWITH A POROUS SURFACE OF A FILTER MATERIAL HAVING A POROSITY AT LEAST ASFINE AS WOOL FELT, AND THEN FORCING THE ORGANIC SOLVENT UNDER A FLUIDPRESSURE DIFFERENTIAL THROUGH THE SKIN IN THE DIRECTION SUCH THAT THESOLVENT FLOWS FROM THE SKIN TO THE SURFACE.